This invention relates to methods of making metal castings, particularly to the incorporation of riser sleeves into a sand mold during the preparation of the mold for receiving molten metal in the formation of metal castings.
The use of riser sleeves are well known in the prior art. Riser sleeves are used as a conduit within which molten metal is accumulated before the molten metal ultimately flows from the riser sleeve into a preformed cavity within a mold. Riser sleeves are manufactured from heat insulating materials to prevent the molten metal from solidifying within the riser sleeve before it passes to the preformed cavity. Typically, riser sleeves are manufactured from heat insulating refractory materials, including man-made fibers. Riser sleeves can include fuels such as aluminum or silicon which are used to produce their respective heat insulating oxides during an exothermic reaction within the riser sleeve. Riser sleeves are produced to have low densities and high porosities to provide additional good heat insulating properties.
There are two major types of riser sleeves in the prior art: open top riser sleeves and blind riser sleeves. Blind riser sleeves comprise a hollow dome shaped riser sleeve, whereas open top riser sleeves are generally annular shaped. Blind riser sleeves are more expensive to manufacture and are only used in special applications. Open top riser sleeves allow the casting operator to see the progress of the cast by visualizing the level of the molten metal in the riser sleeve. Because of their prevalence, for purposes of this specification and the claims, the term riser sleeve only refers to open top riser sleeves.
Patterns are used to create a mold cavity conforming to the casting configuration. Riser plugs or riser location plugs, hereinafter referred to as plugs, are used to create the riser passage itself and to locate the riser sleeve in a desired position on the casting. In operation the riser sleeves hold a reservoir of liquid metal in fluid communication with the mold cavity. The plugs are positioned on the casting in a location which provide liquid metal to compensate for the volumetric change which takes place in the cooling metal within the mold cavity.
During the formation of the mold, the plug is positioned adjacent the selected pattern and the prior art riser sleeves are placed on the plug. The plug is made to be slightly smaller than the nominal interior diameter of the riser sleeve. However plugs are typically not symmetrical in shape and gaps between the plug and the interior surface of the riser sleeve are common.
There are two types of molding sand typically used in the preparation of a mold, i.e. xe2x80x9cgreenxe2x80x9d sand and xe2x80x9cno-bakexe2x80x9d sand. Green sand is composed of sand, clays, water and other additives. No-bake sand is composed of sand and bonding agents such as resins, catalysts and other additives to create a chemically bonded self hardening molding sand. Both of these molding sands are placed about the exterior of the pattern assembly by means of hand ramming, machine jolting and squeezing, high pressure squeezing, sand slinging etc. to form the mold. When the molding sand is positioned in this way, it often accumulates in the interstitial space formed by the external surface of the plug and the internal surface of the riser sleeve. In the case of the self hardening no-bake sand, when the molding sand hardens it is difficult to remove the plug from the riser sleeve without hammering the plug from the sleeve or otherwise coercing it. When such coercive forces are used on the plug, or pattern assembly the plug and pattern may become damaged requiring repair. Also the vibration from the coercive forces causes the riser sleeve to become loosened from the surrounding molding medium causing it to shift during pouring, producing an undesired lump or fin on the casting which must be removed by grinding or other removal method.
This prior art riser sleeve can also produce quality control problems. The molding sand which accumulates in the interstitial space between the riser sleeve and the plug must be removed. The accumulated molding sand is most often a thin layer of sand left adhered to the internal wall of the riser sleeve after the plug is removed. The frequency which this layer of sand is formed is such that a position on the metal casting assembly line is dedicated to the task of removing it. This sand layer is removed with the aid of implements such as a molder""s trowel or file. The removal is necessary to prevent the sand from later falling into the mold cavity during movement of mold or while the mold is filled with molten metal. Any sand which so enters the mold cavity creates unwanted inclusions and unacceptable metallurgical imperfections which must be removed from the casting after it has cooled. This removal process is very time consuming and costly.
Thus, there exists a need in the prior art for a sealing apparatus to prevent molding sand from entering the passage within the riser sleeve.
An object of the present invention is to provide a riser sleeve apparatus which prevents molding sand from entering the interstitial space between a riser sleeve and the plug of a cast pattern.
A further object of the present invention is to provide a riser sleeve apparatus which reduces the time for preparing a metal molding, by allowing for the easy stripping of the pattern and plug.
A further object of the present invention is to provide a riser sleeve apparatus which eliminates impurities in the finished cast product by preventing molding sand from entering the mold cavity prior to and during metal pouring.
A further object of the present invention is to provide a riser sleeve apparatus which eliminates the need to remove accumulated sand from the interior of the riser sleeve prior to metal pouring.
A further object of the present invention is to provide a riser sleeve apparatus which is easy to use and to manufacture.
Further objects of the present invention will be made apparent in the following Best Modes for Carrying Out Invention and the appended Claims.
The foregoing objects are accomplished in the preferred embodiment of the invention by a riser sleeve apparatus which is used for preparing and insulating a passage within which molten metal is accumulated prior to its movement into a mold cavity. The riser sleeve comprises an inner surface which longitudinally extends between an open first end and an open second end. The inner surface bounds the molten metal passage.
The riser sleeve further comprises an annular lip which is positioned adjacent the inner surface and extends inward into the passage. The annular lip includes an engagement edge which is deformable. The annular lip further includes a lower surface and a top surface. The lower surface extends from the inner surface at a generally 45xc2x0 angle. The top surface is an extension of the second end. Thus, the annular lip extends from the inner surface adjacent the second end.
The annular lip is adapted for engagement with an exterior surface of any article extending through the passages, such as a plug. The annular lip deforms to engage the article about the perimeter of the article sealing the area above the second end from the interstitial space created between the article and the inner surface.
The first end of the riser sleeve is adapted to facilitate fluid communication between the passage and the mold cavity. The first end extends at an angle generally normal to the inner surface to allow engagement of the first end with the top surface of a pattern. This engagement seals the passage adjacent the first end from any molding sand placed about the riser sleeve and pattern.
The riser sleeve is generally manufactured from fibrous refractory material. The riser sleeve is manufactured by vacuum forming the refractory material from a slurry onto a preformed mesh. The riser sleeve is used in a process for forming a metal cast comprising the steps of first positioning the riser sleeve about a plug of a pattern assembly. The plug can be screwed or otherwise fastened upon the top surface of the selected pattern. When the riser sleeve is placed upon the plug it is secured about the plug so that the annular lip of the riser sleeve engages an exterior surface of the plug. To secure the riser sleeve, the riser sleeve is moved toward the plug while annular lip moves past the external surface of the plug deforming the annular lip. When the annular lip is so deformed, the engagement edge of the annular lip seals against the external surface about the entire perimeter of the external surface. The preferred method of so securing the riser sleeve onto the plug is to rotate the riser sleeve relative the plug which causes the annular lip to deform about the external surface of the plug and to seal about the perimeter of the plug.
When the riser sleeve is so secured, its longitudinal position is fixed and the first end is also sealed against the top surface of the pattern. With the passage of the riser sleeve sealed at both the first and second ends, molding sand can be formed about the exterior of the pattern and the riser sleeve. Molding sand is prevented from entering the interstitial space between the riser sleeve and the plug by the annular lip.
When the molding sand is hardened, the pattern with the plug is stripped from the interior of the molding sand leaving a mold cavity which is formed by the pattern. The passage within the riser sleeve is left in communication with the formed mold cavity. By preventing the accumulation of molding sand within the interstitial space the plug is stripped from the passage with relative ease. When the mold thus assembled, metal can be cast by pouring it into the mold cavity.
In a preferred embodiment for manufacturing the sealing riser sleeve, the process of vacuum forming is utilized. The process for vacuum forming a sealing riser sleeve comprising the steps of slurrying a mixture of heat insulating materials in a container. A perforated former is then lowered into the mixture. The perforated former includes a first surface and a second surface. The perforated former includes a groove about the perimeter of the first surface. The second surface of the perforated former is in operative communication with a vacuum source. The vacuum source can be selectively put into and out of fluid communication with the second surface. When the vacuum source is in communication with the second surface it causes the heat insulating materials within the slurry to deposit on the first side of the perforated former. The deposited materials form a sealing riser sleeve. When the desired thickness of heat insulating materials is deposited, the communication of the vacuum source with the second surface is stopped, and the formed sealing riser sleeve is removed from the perforated former. The formed sealing riser sleeve includes an annular lip formed by the groove.